1. Alcohols, Ethers and Thiols
Bettelheim, Brown, Campbell and Farrell
Chapter 14

2. Review of Carbon Classification
Type of C Attached to 1o (primary) C one other carbon 2o (secondary) C two other carbons 3o (tertiary) C three other carbons 4o (quaternary) C four other carbons

3. Alcohols
Alcohol: Has an -OH (hydroxyl) group bonded to a tetrahedral carbon
methanol, CH3OH, is the simplest alcohol

4. Classification of Alcohols
Depends on the C which has the –OH group attached
1o Alcohol—attached to one C
2o Alcohol—
attached to
two Cs
3o Alcohol--
attached to three Cs

5. Alcohol Nomenclature
1.Find longest carbon chain that contains the -OH group (parent chain)
2.Number chain from end that gives the -OH the lower number
3.Change the ending -e to -ol
4.Use a number to show the location of the -OH group
For cyclic alcohols, the carbon with the -OH group is C-1
5.Name and number substituents and list them in alphabetical order

6. Nomenclature

7. Nomenclature
Write the IUPAC name for each alcohol

8. Nomenclature

9. Nomenclature
Alcohols containing more than one hydroxyl groups are named as a diol, a triol, and so on
IUPAC names for diols, triols, and so on retain the final "-e" in the name of the parent alkane
Compounds containing two hydroxyl groups on adjacent carbons are commonly called glycols

10. Name the following

11. Name the following
trans-1,3-cyclohexanediol
1,3-propanediol

12. Physical Properties Alcohols are polar molecules
the C-O and O-H bonds are both polar covalent

13. Physical Properties Alcohols can also form hydrogen bonds with water
Alcohol molecules can form hydrogen bonds with each other
Alcohols can also form hydrogen bonds with water

14. Physical Properties of Alcohols
Boiling point increases as MW increases
Solubility in water decreases as MW increases

15. Chemical Properties of Alcohols
Combustion Reactions (they burn in O2)
Acid-Base Chemistry
Dehydration
Oxidation

16. Acidity of Alcohols Alcohols have about the same pKa values as water
Aqueous solutions of alcohols have the same pH as that of pure water
Phenols have lower pKa values than normal alcohols do (are more acidic)

17. Acidity of Alcohols Alcohols and phenols both contain an OH group
Phenols are weak acids and react with strong bases such as NaOH to form water-soluble salts
pKa = 9.89 for phenol
Alcohols are much weaker acids and do not react in this manner

18. Why are phenols more acidic than alcohols
Why are phenols more acidic than alcohols? Aromatic ring and O have delocalization of electrons. Less pull on H, so it is more acidic.

19. Dehydration
Dehydration: Removal of water from adjacent carbons to form an alkene
most often occurs by heating an alcohol with either 85% H3PO4 or concentrated H2SO4

20. Dehydration essentially the reverse of hydration (addition of water to double bond)
Conditions required depend on kind of alcohol

21. Acid-Catalyzed Dehydration
1o ca 180oC needed
Hard
2o lower temperatures
Moderate
3o slightly above room temperature
Easy

22. Dehydration
Zaitsev’s Rule: When two alkene products are possible, the alkene having the greater number of alkyl groups (i.e., C atoms) on the double bond generally predominates (forms major product)
Major product favored.
(minor product)

24. Dehydration-Hydration Related
Acid-catalyzed hydration of alkenes and acid-catalyzed dehydration of alcohols are competing reactions
Equilibrium between alkene and alcohol exists
Large amounts of water favor alcohol formation, while removal of water from the equilibrium mixture favors alkene formation (Le Chatelier's principle)

25. Dehydration vs Oxidation
Dehydration: Remove –OH and –H
OH from one C: H from adjacent C
Oxidation: Remove two –H atoms
One H from OH group: Other H from C that has the –OH attached

26. Oxidation of Alcohols
Oxidation of a 1° alcohol gives an aldehyde or a carboxylic acid, depending on the experimental conditions
Oxidation of a 1° alcohol to a carboxylic acid is carried out using an oxidizing agent such as potassium dichromate, K2Cr2O7, in aqueous sulfuric acid

27. Oxidation of Alcohols
Can sometimes stop the oxidation at the aldehyde stage by distilling the mixture (Aldehydes usually have lower boiling points than either the 1° alcohol or the carboxylic acid)
Alcohol
Aldehyde
Carboxylic acid

28. Oxidation of Alcohol Oxidation of a 2° alcohol gives a ketone
Tertiary alcohols are resistant to oxidation

29. Oxidation of Alcohols
Draw a structural formula for the product formed by oxidation of each of the following alcohols with potassium dichromate.
a) 1-Hexanol b) 2-Hexanol
Strategy
Oxidation of 1-hexanol, a primary alcohol, gives either an aldehyde or a carboxylic acid, depending on the experimental conditions. Oxidation of 2-hexanol, a secondary alcohol, gives a ketone.

30. Solution
(a) or
Hexanal Hexanoic acid
(b)
2- Hexanone

31. Common Alcohols Ethanol Ethyl alcohol, “grain alcohol”
Produced by fermentation
Natural fermentation of sugars and starches in grains, corn, molasses, fruits, vegetables
Found in beer, wine, and other “spirits”
C6H12O6 → 2 CH3CH2OH + 2 CO2
glucose ethanol carbon dioxide

32. Common Alcohols Methanol Methyl alcohol or “wood alcohol”
Distilled from wood pulp originally
Very toxic, even in small amounts
Reacts to make formaldehyde (a fixative)
CH3OH → CH2=O
methanol formaldehyde

33. Common Alcohols Isopropyl alcohol 2-propanol “rubbing alcohol”
Evaporates quickly—used to reduce fever
Solvent in many cosmetics, perfumes, etc.

34. Common Alcohols 1,2-ethanediol Glycerol Ethylene glycol
Very soluble in water
Used as antifreeze
Glycerol
1,2,3-propanetriol
Sweet taste
Part of fats and oils

35. Preparation of Important Alcohols
Many alcohols (or their derivatives) can be formed by reacting smaller molecules.

36. Preparation of Important Alcohols

37. Ethers
The functional group of an ether is an oxygen atom bonded to two carbon atoms
Simplest ether is dimethyl ether
Most common ether is diethyl ether
Often called just “ether”

38. Ether Nomenclature
Generally use common names for small (low-molecular-weight) ethers
common names are derived by listing the alkyl groups bonded to oxygen in alphabetical order and adding the word "ether”
alternatively, name one of the groups on oxygen as an alkoxy group

39. Ether Nomenclature
Cyclic ether: an ether in which one of the atoms in a ring is oxygen
Cyclic ethers also known by their common names
ethylene oxide is an important building block for the organic chemical industry; it is also used as a fumigant in foodstuffs and textiles, and in hospitals to sterilize surgical instruments
tetrahydrofuran is a useful laboratory and industrial solvent

40. Physical Properties of Ethers
Ethers are polar compounds
O has a partial negative charge
Each C bonded to it has a partial positive charge
Only weak forces of attraction exist between ether molecules in the pure liquid
Boiling points of ethers are close to those of hydrocarbons of similar molecular weight
Have lower boiling points than alcohols of the same molecular formula

41. Reactions of Ethers Ethers not very reactive (like hydrocarbons)
Do not react with oxidizing agents such as potassium dichromate
Do not react with reducing agents such as H2 in the presence of a transition metal catalyst
Not affected by most acids or bases at moderate temperatures
Good solvents for carrying out organic reactions, because of their general inertness and good solvent properties
Diethyl ether and THF (tetrahydrofuran)

42. Thiols Thiol: a compound containing an -SH (sulfhydryl) group
Also called mercaptans
Low-molecular-weight thiols STINK
Responsible for smells such as those from rotten eggs and sewage
the scent of skunks is due primarily to these two thiols

43. Thiols - Nomenclature
IUPAC names are derived in the same manner as are the names of alcohols
Retain the final -e of the parent alkane and add the suffix -thiol
Common names for simple thiols are derived by naming the alkyl group bonded to -SH and adding the word "mercaptan"

44. Thiol Physical Properties
S-H bonds are nonpolar covalent
Small difference in electronegativity between sulfur and hydrogen ( = 0.4)
No hydrogen bonding
Lower boiling points than comparable alcohols
Less soluble in water and other polar solvents than comparable alcohols

45. Reactions of Thiols
Thiols are weak acids (pKa~10), and are comparable in strength to phenols
thiols react with strong bases such as NaOH to form water-soluble thiolate salts

46. Reactions of Thiols
The most important thiol reaction in biological systems is their oxidation to disulfides
Functional group is a disulfide (-S-S-) bond
Disulfide bonds important in protein structure
Thiols are readily oxidized to disulfides by O2
-SH group very susceptible to oxidation and must be protected from contact with air during storage
disulfides, in turn, are easily reduced to thiols by several reducing agents.

47. Reactions of Thiols Oxidation of –SH groups to form S-S bonds Reduction of S-S bonds to form –SH groups